Within the last few years there has been significant interest in the development of gas slab lasers. As described in U.S. Pat. No. 5,123,028 (assigned to the same assignee herein and incorporated by reference), these type of lasers preferably include a pair of planar, rectangular electrodes, spaced apart in a manner to define a slab discharge region. The slab discharge region has a narrow axis extending between the electrodes and a wider axis extending parallel to the electrode surfaces. In the preferred embodiment, the narrow axis defines a waveguide channel between the electrodes.
A lasing gas, such as carbon dioxide, is located between the electrodes. A means is provided for energizing the electrodes to excite the gas. In the illustrated embodiment, the lasing gas is excited with an RF generator. A mirror is positioned adjacent each end of the electrodes to define the resonator.
In order to maximize the power output and enhance stability in a slab laser, it is desirable to employ a "hybrid" resonator. In a hybrid resonator, the propagation of light in one axis is different from the propagation of light in the other axis. As noted above, in the narrow axis, a stable waveguide resonator is defined. In contrast, in the wider axis, a free-space resonator is defined. Where the width of the wider axis is a few centimeters or more, the free-space resonator is defined by an unstable resonator. In the preferred design, a negative branch unstable resonator is used. In addition, one of the end mirrors of the resonator is slightly shorter than the other end mirror, so that laser beam can be "edge coupled" out of the resonator.
The assignee herein has successfully marketed lasers designed in accordance with the above cited patent, both for use in medical systems (sold under the trademark "Ultrapulse") and for industrial applications (sold under the trademark "Diamond".) Significant research activity has continued in order to further improve this product.
One area which has been investigated relates to the stability of the output power of the laser. As can be seen in the above identified patent, the resonator mirrors are mounted to the ends of a sealed laser housing. As the laser operates, the length of the housing, and hence the length of the resonator, will vary. As the length of the resonator varies, different longitudinal modes of the laser will oscillate in a phenomenon referred to as mode sweeping. It has been found that this mode sweeping phenomenon can result in power fluctuations in excess of ten percent and as much as fifteen percent. These power fluctuations can be detrimental for both medical and industrial applications.
Therefore, it is object of the subject invention, to provide an improved resonator structure which significantly improves the power stability of a carbon dioxide, slab waveguide laser.
It is a further object of the subject invention to provide a new resonator structure that improves alignment stability.
It is another object of the subject invention to provide a new resonator structure that allows the laser to operate with an increased number of longitudinal modes.
It is still a further object of the subject invention to provide a new resonator structure that provides greater tunability for single line operation.
It is still another object of the subject invention to provide a new resonator structure which allows the beam to be coupled out of the center of the slab discharge region rather than along one edge.
It is still a further object of the subject invention to provide an improved resonator structure which allows the width of the discharge region to be expanded while minimizing spherical aberrations induced by the mirrors.
It is still another object of the subject invention to provide an improved resonator structure that can be adapted for use with other lasers having slab-shaped gain regions, such a solid state slab lasers.